Sectorized antennas for improved airborne reception of surveillance signals

ABSTRACT

A plurality of antenna elements may receive a plurality of signals. Each of the plurality of antenna elements may correspond to at least one of a plurality of sectors of a sectorized antenna. A receiver may process each of the plurality of signals in parallel, including decoding one or more messages from the plurality of signals. The receiver may output at least one of the one or more messages.

This application is a continuation of application Ser. No. 14/572,422,filed Dec. 16, 2014 entitled SECTORIZED ANTENNAS FOR IMPROVED AIRBORNERECEPTION OF SURVEILLANCE SIGNALS, the entire contents of which arehereby incorporated by reference herein.

TECHNICAL FIELD

The disclosure relates to airborne reception of surveillance messagesvia sectorized antennas.

BACKGROUND

Automatic dependent surveillance broadcast (ADS-B) is a technology wherea particular aircraft can determine its position and report it (togetherwith other data such as position data accuracy, aircraft identification,barometric altitude, and the like), thereby enabling other aircraft andair traffic control ground stations to be aware of the position of theparticular aircraft. As a result, aircraft and ground stations equippedwith ADS-B receiving devices may determine the positions of otheraircraft that are equipped by ADS-B transmitting devices in theirvicinity. Transmitting and receiving of ADS-B messages by aircraft maysupplement or replace the use of ground-based radars that determine thepositions of airborne aircraft to prevent airborne collisions.

SUMMARY

Devices, systems, and techniques for improving an aircraft's receptionof ADS-B messages are described herein. In some examples, a sectorizedantenna comprising a plurality of directional antenna elements mayreceive one or more signals carrying one or more ADS-B messages. Areceiver operably coupled to the plurality of directional antennaelements may process the one or more signals to decode the one or moreADS-B messages. In one example, the sectorized antenna may receive aplurality of signals carrying a plurality of ADS-B messages. Thereceiver may process the plurality of signals in parallel, includingdecoding the plurality of ADS-B messages carried by the plurality ofsignals in parallel. In some examples, the sectorized antenna may be atraffic collision avoidance system (TCAS) antenna and the signalprocessor that processes the signals received by the antenna may be apart of modified TCAS unit. In this way, the sectorized antennastechnique, as disclosed herein, may be implemented by reusing andmodifying an already-installed TCAS unit included in an aircraft.

A conventional ADS-B receiver system may typically lose a number ofADS-B messages when they are received close enough to overlap,particularly in crowded air traffic conditions such as are increasinglycommon near large airports. In accordance with aspects of the presentdisclosure, the sectorized antennas technique disclosed herein mayreduce the number of lost ADS-B messages due to overlapping signals,which may prevent a degradation of any applications that use ADS-Bmessage data carried by the ADS-B messages, including, for example,applications involved in collision avoidance and situational awareness.

In one example, the disclosure is directed to a method. The methodcomprises receiving, by a plurality of antenna elements, a plurality ofsignals, wherein each of the plurality of antenna elements correspond toat least one of a plurality of sectors of a sectorized antenna. Themethod further comprises processing, by a receiver, each of theplurality of signals, including decoding one or more messages from theplurality of signals. The method further comprises outputting, by thereceiver, at least one of the one or more messages.

In another example, the disclosure is directed to a system. The systemcomprises a plurality of antenna elements configured to receive aplurality of signals, wherein each of the plurality of antenna elementscorresponds to at least one of a plurality of sectors of a sectorizedantenna. The system further comprises a receiver configured to: processeach of the plurality of signals in parallel, including decoding one ormore messages from the plurality of signals; and output at least one ofthe one or more messages.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages in addition to those described below will be apparent fromthe description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a functional block diagram illustrating an example aircraft 2that includes antenna elements 4A-4D which are configured to receivesignals indicative, among others, of the positions of other aircraftwithin a specified vicinity of the example aircraft's position.

FIG. 1B is a functional block diagram illustrating an example receiver8.

FIG. 2 is a functional block diagram illustrating an example receiver 8for receiving and decoding a plurality of messages in parallel.

FIG. 3 is a functional block diagram illustrating an example receiver 8for combining a plurality of signals.

FIG. 4 is a functional block diagram illustrating an example receiver 8for selecting a single signal to decode.

FIG. 5 is a functional block diagram illustrating an example receiver 8for selecting a signal to process.

FIG. 6 is a functional block diagram illustrating the duplicity checkunit 22 of FIG. 2 in further detail.

FIG. 7 is a functional block diagram illustrating the combining unit 24of FIG. 3 in further detail.

FIG. 8 is a flow diagram illustrating an example technique for receivingand decoding messages according to aspects of the present disclosure.

DETAILED DESCRIPTION

Example devices, systems, and techniques for receiving and decodingsurveillance messages are described in this disclosure. Morespecifically, the present disclosure describes example devices, systems,and techniques for an aircraft to improve reception of radio frequency(RF) signals that carry automatic dependent surveillance broadcast(ADS-B) messages that, among others, indicate the positions of one ormore other neighboring aircraft.

In certain geographical areas where air traffic is very dense, two ormore ADS-B messages may sometimes arrive at an antenna of an ADS-Breceiving device at the same time and may therefore overlap. When theoverlapping incident messages have significantly different power levels,the ADS-B receiving device may typically process only the message withthe relatively strongest power level, thereby losing the messages withrelatively weaker power levels. Thus, when the messages are overlapped,at least one message is processed. However, when the overlappingincident messages each have comparable power levels, each of theoverlapped messages may be lost, thereby leading to decreasedfrequency-space utilization and consequently also a decreased ability ofthe system to assure performance measures such as availability requiredby applications utilizing ADS-B messages.

Examples of potential issues an aircraft may encounter with receivingand decoding ADS-B messages may include channel congestion (e.g.,interference). An ADS-B channel may be shared by systems such asdistance measuring equipment (DME) systems, traffic collision avoidancesystems (TCAS), secondary surveillance radar (SSR) systems, and thelike. Channel congestion may also occur due to high traffic density nearlarge airports.

FIG. 1A is a functional block diagram illustrating an example aircraft 2that includes antenna elements 4A-4D (“antenna elements 4”) which areconfigured to receive signals that carry ADS-B messages transmitted byaircraft within a specified vicinity of aircraft 2's position.

Antenna elements 4 may make up a sectorized antenna comprising aplurality of sectors, where each antenna element of antenna element 4may correspond to at least one of the plurality of sectors of thesectorized antenna. As such, each of antenna elements 4A-4D may be adirectional antenna. A directional antenna may be an antenna that doesnot radiate and/or receive signals uniformly in all directions. However,a directional antenna may show a greater gain in one or more directions,thereby increasing its performance in transmitting and receiving signalsin those one or more directions. Each of antenna elements 4A-4D may bepositioned in aircraft 2 such that each of antenna elements 4A-4D mayshow greater gain in a substantially different direction with respect tothe other antenna elements of antenna elements 4. In the example of FIG.1A, because antenna elements 4 comprise four elements 4A-4D, antennaelements 4 may be a sectorized antenna having four sectors, and each ofthe four antenna elements 4A-4D may show greater gain in a substantiallydifferent direction with respect to the other of antenna elements 4A-4D.Although the example of FIG. 1A illustrates a sectorized antenna havingfour antenna elements 4A-4D, it should be understood that a sectorizedantenna in accordance with techniques of the present disclosure mayinclude greater or fewer than four antenna elements. As such, antennaelements 4 may comprise two or more antenna elements with variousdirectional characteristics (radiation patterns).

Antenna elements 4 may be configured to receive analog radio frequency(RF) signals that carry ADS-B messages. In one example, antenna elements4 may operate at an ADS-B channel at 1090 MHz to receive signalscarrying ADS-B messages that indicate, among others, the positions ofone or more other neighboring aircraft.

As shown in FIG. 1A, one or more aircraft in the vicinity of aircraft 2may broadcast RF signals 6A and 6B from differing directions. In someexamples, RF signals 6A and 6B may at least partially overlap in time,such that two or more of antenna elements 4A-4D may be able to receiveone or both of RF signals 6A and 6B. For example, both antenna element4A and antenna element 4C may be able to receive both RF signals 6A and6B. However, due to the directional nature of antenna elements 4 and dueto RF signals 6A and 6B being broadcast from different directions, thecomposite RF signal (a combination of RF signals 6A and 6B) received byindividual antenna elements 4A and 4C may differ (the power ratiosbetween RF signals 6A and 6B), which may increase the probability thatADS-B messages carried by RF signals 6A and 6B respectively will becorrectly decoded. In the example shown in FIG. 1A, RF signal 6Areceived by antenna element 4A is significantly more powerful than RFsignal 6B received by antenna element 4A. Conversely, RF signal 6Breceived by antenna element 4C is significantly more powerful than RFsignal 6A received by antenna element 4C. While the example of FIG. 1Ashows antenna elements 4 receiving two RF signals 6A and 6B, antennaelements 4 may be able to receive fewer or more than two RF signals. Forexample, each of the four elements 4A-4D of antenna elements 4 may beable to receive one or more RF signals which may be the same as ordifferent from RF signals received by other elements of antenna elements4. In the example shown in FIG. 1A, RF signals 6A and 6B may eachrepresent an ADS-B message, may respectively represent a single ADS-Bmessage and an interfering signal, or may represent any other signalsharing the same RF channel.

Aircraft 2 may include receiver 8 which may be operably coupled toantenna elements 4. Receiver 8 may be configured to process one or moreof the plurality of signals received by antenna elements 4, includingdecoding one or more ADS-B messages from the one or more of theplurality of signals. Receiver 8 may be further configured to output theone or more ADS-B messages that it has decoded. For example, receiver 8may output the one or more ADS-B messages that it has decoded to thetraffic computer (not depicted in FIG. 1A). Traffic computer may processADS-B data (among other data inputs) and may output application specificdata to a communication bus (not depicted in FIG. 1A).

FIG. 1B is a functional block diagram illustrating an example receiver8. As shown in FIG. 1B, receiver 8 may include radio frequency front-end(RFFE) 12, analog-to-digital converter (ADC) 14, and digital back-end(DBE) 20.

RFFE 12 may be operably coupled to antenna elements 4 and may processcorresponding RF signal streams received from corresponding antennaelements 4A-4D to convert them into intermediate frequency (IF) signals.As discussed above, an antenna element of antenna elements 4 may receivean RF signal stream that may convey one or more ADS-B messages(corresponding RF signals), and RFFE 12 may be configured to select andprocess the RF signal streams received from one or more of antennaelements 4. In one example, RFFE 12 may select one RF signal streamreceived by one of antenna elements 4 out of all available RF signalstreams received by all of antenna elements 4, based at least in part onthe respective signal power levels of the received RF signal streams,such as selecting the RF signal stream received by one of antennaelements 4 with the highest signal power level (i.e., the strongestsignal) out of all available RF signal streams received by that one ofantenna elements 4.

In some examples, RFFE 12 may include a plurality of RFFEs, each ofwhich corresponds with one of antenna elements 4, or may include amulti-channel RFFE, where each channel of the multi-channel RFFEcorresponds with one of antenna elements 4. For example, if antennaelements 4 comprise four antenna elements 4A-4D, RFFE 12 may includefour RFFEs or may include a four-channel RFFE. In this way, RFFE 12 maybe able to process RF signal streams received from two or more antennaelements of antenna elements 4 in parallel, such that RFFE 12 may beable to process multiple RF signal streams from two or more antennaelements of antenna elements 4 at the same time instead of processingjust a single RF signal stream. It should be understood that the termparallel as used throughout this disclosure should not necessarilyindicate any precise overlap or perfect synchronization in processingmultiple RF signal streams.

Thus, in the example of FIG. 1B, a first channel of RFFE 12 maycorrespond to antenna element 4A and a second channel of RFFE 12 maycorrespond to antenna element 4C. The first channel of RFFE 12 mayprocess and convert the corresponding RF signal stream into an IFsignal. Correspondingly, a second channel of RFFE 12 may process andconvert the corresponding RF signal stream into an IF signal. The firstand second channels of RFFE 12 may operate to process the RF signalstreams from antenna elements 4A and 4C in parallel.

ADC 14 may be operably coupled to RFFE 12 and may convert analogintermediate frequency signals received from RFFE 12 to digitalintermediate frequency signals, and may output the digital intermediatefrequency signals to DBE 20. Similar to RFFE 12, ADC 14 may include aplurality of ADCs or may be a multi-channel ADC, such that each of theplurality of ADCs or each channel of the multi-channel ADC may processanalog IF signals outputted by a corresponding channel of amulti-channel RFFE 12 or by one of a plurality of RFFEs of RFFE 12.

DBE 20 may be operably coupled to ADC 14 and may continuously attempt todetect and decode ADS-B messages contained in the digital signal streamsoutputted by ADC 14 in parallel. Detection and decoding may beperformed, in one non-limiting example, in accordance with the DO-260Bstandard (or EUROCAE ED-102A, which is the European equivalent)promulgated by the Radio Technical Commission for Aeronautics (RTCA) andthe Federal Aviation Administration (FAA). DBE 20 may include aplurality of DBEs or may be a multi-channel DBE. ADS-B message detectionand decoding may be performed separately for each channel. As individualdigital signal streams received by individual antenna elements 4 maydiffer (such as by amplitude of individual received ADS-B messages), theADS-B message detection and decoding algorithm performed in all channelsof DBE 20 may detect and decode various messages in each DBE channel.

DBE 20 may be operably coupled to ADC 14 and may be to decode one ormore ADS-B messages contained in the digital signals outputted by ADC 14in parallel. Decoding one or more ADS-B messages contained in thedigital signals in parallel is not limited to starting decoding ofmultiple signals or outputting one or more ADS-B messages exactly at thesame time. For example, if DBE 20 starts processing a first digitalsignal outputted by ADC 14 and, while processing the first digitalsignal, then starts to process a second digital signal outputted by ADC14, DBE 20 may still be deemed to be processing the first and seconddigital signals in parallel, in that DBE 20 may be able to process morethan one digital signal at the same time. The first signal maycorrespond, for example, to the RF signal 6A (depicted in FIG. 1A)received by antenna element 4A and the second signal may correspond, forexample, to the RF signal 6B (depicted in FIG. 1A) received by antennaelement 4C. As such, the term parallel should not necessarily indicateany precise overlap or perfect synchronization in processing multipledigital signals.

As discussed in further detail below, DBE 20 may process the digital IFsignals outputted by ADC 14 to convert the digital IF signals intobaseband signals and may also detect and decode ADS-B messages carriedby the baseband signals. DBE 20 may output the decoded ADS-B messagedata to, for example, a traffic computer (not depicted in FIG. 1B).Similar to RFFE 12 and ADC 14, DBE 20 may include a plurality of DBEs ormay be a multi-channel DBE, such that each of the plurality of DBEs oreach channel of the multi-channel DBE may process digital IF signalsoutputted by a corresponding channel of a multi-channel ADC 14 or by oneof a plurality of ADCs of ADC 14.

The traffic computer of aircraft 2 may process ADS-B data (among otherdata inputs) outputted by receiver 8 and may output application specificdata to a communication bus (not depicted in FIG. 1B). For example, thetraffic computer may output positions of nearby aircraft to acommunication bus. That data may be utilized either by an output device,such as a display device, which may be viewed by pilots of aircraft 2,or it may be processed by a software application, such as a collisionavoidance application.

FIG. 2 is a functional block diagram illustrating an example receiver 8for decoding a plurality of messages in parallel. Receiver 8 may includeRFFE 12, ADC 14, and DBE 20. DBE 20 may include preprocessing unit 16,message detection and decoding unit 18, and duplicity check unit 22.

Receiver 8 may comprise any suitable arrangement of hardware, software,firmware, or any combination thereof, to perform the techniquesattributed to receiver 8, RFFE 12, ADC 14, preprocessing unit 16,message detection and decoding unit 18, DBE 20, and duplicity check unit22 herein. For example, receiver 8 may include any one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs), orany other equivalent integrated or discrete logic circuitry, as well asany combinations of such components. Although RFFE 12, ADC 14,preprocessing unit 16, message detection and decoding unit 18, andduplicity check unit 22 are described as separate modules, in someexamples, RFFE 12, ADC 14, preprocessing unit 16, message detection anddecoding unit 18, and duplicity check unit 22 can be functionallyintegrated. For example, preprocessing unit 16, message detection anddecoding unit 18, and duplicity check unit 22 may be implemented in thesame hardware component. In some examples, RFFE 12, ADC 14,preprocessing unit 16, message detection and decoding unit 18, andduplicity check unit 22 may correspond to individual hardware units,such as ASICs, DSPs, FPGAs, or other hardware units, or one or morecommon hardware units.

Receiver 8 may, in the example of FIG. 2, be considered a parallelreceiver because receiver 8 may fully process each of a plurality of RFsignal streams received by receiver 8 from antenna elements 4 to decodeone or more of the ADS-B messages carried by the RF signal streams inparallel. For example, preprocessing unit 16 may convert, in parallel, aplurality of digital representations of IF signals outputted by ADC 14into a plurality of baseband signals, and message detection and decodingunit 18 may process the plurality of baseband signals outputted bypreprocessing unit 16 in parallel to detect and decode ADS-B messagescarried by the plurality of baseband signals. In this way, DBE 20 may beable to process two or more signals received from ADC 14 at the sametime.

Antenna elements 4, in some examples, may comprise antenna elements of aTCAS antenna. Each element of antenna elements 4 may be a directionalantenna element that corresponds to at least one of a plurality ofsectors of a sectorized antenna. Each of antenna elements 4 may beoperably coupled to RFFE 12 in receiver 8 via, for example, coaxialcables 10A-10D (“coaxial cables 10”) or any other suitable means forconnecting antenna elements 4 to RFFE 12.

RFFE 12 of receiver 8 may, as discussed above, be a multi-channel RFFEthat is operably coupled to antenna elements 4 via, for example, coaxialcables 10. Each channel of RFFE 12 may be associated with a differentantenna element of antenna element 4, and each channel of RFFE 12 mayprocess and convert RF signal streams received from the associatedantenna element of antenna elements 4 into intermediate frequency (IF)signals. For example, each channel of RFFE 12 may receive one RF signalstream from its associated antenna element of antenna elements 4,process and convert the RF signal stream into an analog IF signal.

ADC 14 of receiver 8 may, as discussed above, be a multi-channel ADCthat is operably coupled to RFFE 12. Each channel of ADC 14 may beassociated with a different channel of RFFE 12 to receive an analog IFsignal from the associated channel of RFFE 12 and to convert thereceived analog IF signal into a digital representation of the IFsignal.

Preprocessing unit 16 may be configured to perform filtering,decimation, and downconversion of the digital representations of IFsignals into baseband signals.

Message detection and decoding unit 18 may be configured to performpreamble detection to detect the presence of ADS-B messages within thereceived data stream. Message detection and decoding unit 18 may also beconfigured to decode the ADS-B messages detected within the receiveddata stream. For example, message detection and decoding unit 18 may beconfigured to perform pulse-position modulation (PPM) signaldemodulation into binary data and to perform error detection andcorrection on the demodulated binary data to decode the data content ofADS-B messages (ADS-B data).

Duplicity check unit 22 may be included in DBE 20, may be operablycoupled to message detection and decoding unit 18, and may be configuredto determine whether two or more of the ADS-B messages decoded andoutputted by message detection and decoding unit 18 are identical. Insome examples, receiver 8 may receive duplicate ADS-B messages becausetwo or more of antenna elements 4A-4D may receive RF signals that arecarrying the same ADS-B message.

Duplicity check unit 22 may deem ADS-B messages to be identical if theirparity bits are identical and/or if their data bits are identical. Forexample, identical ADS-B messages may be identified comparing theirparity bits, as the parity bits, obtained by a cyclic redundancy check(CRC) algorithm, may be considered as unique for each ADS-B message.Responsive to determining that two or more ADS-B messages decoded andoutputted by message detection and decoding unit 18 are the same ADS-Bmessage, duplicity check unit 22 may output just one ADS-B message outof the two or more identical ADS-B messages. In other words, duplicitycheck unit 22 may refrain from outputting more than one of two or moreof the same ADS-B messages. Aspects of duplicity check unit 22 will bedescribed in further detail below with respect to FIG. 6.

The example receiver 8 shown in FIG. 2, where a plurality of messagesare decoded in parallel, may be relatively more complex than theexamples of receivers shown in FIG. 3, FIG. 4 and FIG. 5, as the examplereceiver 8 shown in FIG. 2 may utilize multi-channel processing,including multi-channel RFFE 12, multi-channel ADC 14, and multi-channelDBE 20 including an additional duplicity check unit 22.

The traffic computer (not depicted in FIG. 2) of aircraft 2 may processADS-B data (among other data inputs) outputted by receiver 8 and mayoutput application specific data to a communication bus (not depicted inFIG. 2). For example, traffic computer may output positions of nearbyaircraft to a communication bus. That data may be utilized either by anoutput device, such as a display device, which may be viewed by pilotsof aircraft 2, or it may be processed by a software application, such asa collision avoidance application.

FIG. 3 is a functional block diagram illustrating an example receiver 8for combining a plurality of signals. As shown in FIG. 3, receiver 8 maycontain additional combining unit 24. Receiver 8 may include RFFE 12,ADC 14, and DBE 20. DBE 20 may include additional combining unit 24,preprocessing unit 16, and message detection and decoding unit 18.

Receiver 8 may comprise any suitable arrangement of hardware, software,firmware, or any combination thereof, to perform the techniquesattributed to receiver 8, RFFE 12, ADC 14, preprocessing unit 16,message detection and decoding unit 18, DBE 20, and combining unit 24herein. For example, receiver 8 may include any one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs), orany other equivalent integrated or discrete logic circuitry, as well asany combinations of such components. Although RFFE 12, ADC 14,preprocessing unit 16, message detection and decoding unit 18, andcombining unit 24 are described as separate modules, in some examples,RFFE 12, ADC 14, preprocessing unit 16, message detection and decodingunit 18, and combining unit 24 can be functionally integrated. Forexample, preprocessing unit 16, message detection and decoding unit 18,and combining unit 24 may be implemented in the same hardware component.In some examples, RFFE 12, ADC 14, preprocessing unit 16, messagedetection and decoding unit 18, and combining unit 24 may correspond toindividual hardware units, such as ASICs, DSPs, FPGAs, or other hardwareunits, or one or more common hardware units. In some examples, combiningunit 24 may be integrated into DBE 20, preprocessing unit 16, and/ormessage detection and decoding unit 18.

In the example of FIG. 3, two or more antenna elements of antennaelements 4 may each receive an RF signal that carries the same ADS-Bmessage. For example, two or more antenna elements of antenna elements 4may each receive the RF signal that may be different for each antennaelement of antenna elements 4 due to directional characteristics ofindividual antenna elements of antenna elements 4. Receiver 8 maycombine the representations of the RF signal as received by the two ormore antenna elements of antenna elements 4 in order to create a such acombined signal, that the probability of ADS-B message decoding by DBE20 may be higher compared to the probability of ADS-B message decodingfor individual RF signal received by the two or more antenna elements ofantenna elements 4.

Antenna elements 4, in some examples, may comprise antenna elements of aTCAS antenna. Each element of antenna elements 4 may be a directionalantenna element that corresponds to at least one of a plurality ofsectors of a sectorized antenna. Each of antenna elements 4 may beoperably coupled to RFFE 12 in receiver 8 via, for example, coaxialcables 10A-10D (“coaxial cables 10”) or any other suitable means forconnecting antenna elements 4 to RFFE 12.

RFFE 12 of receiver 8 may, as discussed above, be a multi-channel RFFEthat is operably coupled to antenna elements 4 via, for example, coaxialcables 10. Each channel of RFFE 12 may be associated with a differentantenna element of antenna element 4, and each channel of RFFE 12 mayprocess RF signal received from the associated antenna element ofantenna elements 4 and convert it into intermediate frequency (IF)signal. For example, each channel of RFFE 12 may receive one RF signalstream from its associated antenna element of antenna elements 4,process and convert the RF signal stream into an analog IF signal.

As discussed above, two or more antenna elements of antenna elements 4may each receive an RF signal that carries the same ADS-B message. Forexample, each of the four antenna elements 4A-4D of FIG. 3 may receivethe same RF signal that is carrying the same ADS-B message. However, dueto the signal strength, directionality, and other quality considerationsof the same RF signal, each of the four analog IF signals outputted byRFFE 12 may not be identical.

ADC 14 of receiver 8 may, as discussed above, be a multi-channel ADCthat is operably coupled to RFFE 12. Each channel of ADC 14 may beassociated with a different channel of RFFE 12 to receive an analog IFsignal from the associated channel of RFFE 12 and to convert thereceived analog IF signal into a digital representation of the IFsignal. As discussed above, each of all analog IF signals outputted byRFFE 12 may not be identical. Similarly, because each of all analog IFsignals outputted by RFFE 12 may not be identical, each of the digitalrepresentations of the IF signals outputted by ADC 14 may not beidentical.

Combining unit 24 may be configured to combine the digitalrepresentations of IF signals outputted by ADC 14 into a single digitalIF signal that may be processed by single-channel DBE 20. Combining unit24 may perform a linear combination of each of the digitalrepresentations of the IF signals outputted by ADC 14. Combining unit 24may perform phase compensation on the digital representations of IFsignals outputted by ADC 14 to result in a single digital representationof an IF signal. Aspects of combining unit 24 will be described infurther detail below with respect to FIG. 7.

Preprocessing unit 16 may be configured to perform filtering,decimation, and downconversion of the digital representation of the IFsignal into a baseband signal.

Message detection and decoding unit 18 may be configured to performpreamble detection to detect the presence of ADS-B messages within thebaseband signal. Message detection and decoding unit 18 may also beconfigured to decode the ADS-B messages detected within the basebandsignal. For example, message detection and decoding unit 18 may beconfigured to perform pulse-position modulation (PPM) signaldemodulation into binary data and to perform error detection andcorrection on the demodulated binary data to decode the ADS-B data.

Configuration of receiver 8 shown in FIG. 3 may utilize multi-channelRFFE 12, multi-channel ADC 14, combining unit 24, and single-channel DBE20. This configuration may be less complex than the one shown in FIG. 2as it may utilize just single-channel DBE 20 in comparison to themulti-channel DBE shown in FIG. 2.

Traffic computer (not depicted in FIG. 3) of aircraft 2 may processADS-B data (among other data inputs) outputted by receiver 8 and mayoutput application specific data to a communication bus (not depicted inFIG. 3). For example, traffic computer may output positions of nearbyaircraft to a communication bus. That data may be utilized either by anoutput device, such as a display device, which may be viewed by pilotsof aircraft 2, or it may be processed by a software application, such asa collision avoidance application.

FIG. 4 is a functional block diagram illustrating an example receiver 8for selecting a single signal to decode. As shown in FIG. 4, receiver 8may include RFFE 12, ADC 14, and DBE 20. DBE 20 may include selectionunit 25, preprocessing unit 16, and message detection and decoding unit18.

Receiver 8 may comprise any suitable arrangement of hardware, software,firmware, or any combination thereof, to perform the techniquesattributed to receiver 8, RFFE 12, ADC 14, preprocessing unit 16,message detection and decoding unit 18, DBE 20, and selection unit 25herein. For example, receiver 8 may include any one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs), orany other equivalent integrated or discrete logic circuitry, as well asany combinations of such components. Although RFFE 12, ADC 14,preprocessing unit 16, message detection and decoding unit 18, andselection unit 25 are described as separate modules, in some examples,RFFE 12, ADC 14, preprocessing unit 16, message detection and decodingunit 18, and selection unit 25 can be functionally integrated. Forexample, preprocessing unit 16, message detection and decoding unit 18,and selection unit 25 may be implemented in the same hardware component.In some examples, RFFE 12, ADC 14, preprocessing unit 16, messagedetection and decoding unit 18, and selection unit 25 may correspond toindividual hardware units, such as ASICs, DSPs, FPGAs, or other hardwareunits, or one or more common hardware units.

Antenna elements 4, in some examples, may comprise antenna elements of aTCAS antenna. Each element of antenna elements 4 may be a directionalantenna element that corresponds to at least one of a plurality ofsectors of a sectorized antenna. Each of antenna elements 4 may beoperably coupled to RFFE 12 in receiver 8 via, for example, coaxialcables 10A-10D (“coaxial cables 10”) or any other suitable means forconnecting antenna elements 4 to RFFE 12.

RFFE 12 of receiver 8 may, as discussed above, be a multi-channel RFFEthat is operably coupled to antenna elements 4 via, for example, coaxialcables 10. Each channel of RFFE 12 may be associated with a differentantenna element of antenna element 4, and each channel of RFFE 12 mayprocess and convert RF signal stream received from the associatedantenna element of antenna elements 4 into intermediate frequency (IF)signal. For example, each channel of RFFE 12 may receive one RF signalstream from its associated antenna element of antenna elements 4,process and convert the associated RF signal stream into an analog IFsignal.

ADC 14 of receiver 8 may, as discussed above, be a multi-channel ADCthat is operably coupled to RFFE 12. Each channel of ADC 14 may beassociated with a different channel of RFFE 12 to receive an analog IFsignal from the associated channel of RFFE 12 and to convert thereceived analog IF signal into a digital representation of the IFsignal.

Selection unit 25 may be configured to select one of the digitalrepresentations of the IF signals outputted by ADC 14 for furtherprocessing by preprocessing unit 16 and message detection and decodingunit 18. For example, selection unit 25 may select the strongest signal(e.g., signal with the highest power level) out of the digitalrepresentations of the IF signals outputted by ADC 14. In otherexamples, selection unit 25 may be integrated into or otherwise beoperably coupled to message detection and decoding unit 18 so thatselection unit 25 may utilize message detection and decoding unit 18 todetermine if the signal selection unit 25 selects signal that includesan ADS-B message. Because antenna elements 4 may receive signals that donot carry ADS-B messages, selection unit 25 may select a signal thatdoes not carry an ADS-B message if selection unit 25 does not alsoutilize message detection and decoding unit 18 to determine if thesignal selection unit 25 selects signal that includes an ADS-B message.If selection unit 25 is integrated into or otherwise be operably coupledto message detection and decoding unit 18, selection unit 25 may beconfigured to select one of the baseband signals outputted bypreprocessing unit 16.

Preprocessing unit 16 may be configured to perform filtering,decimation, and downconversion of the digital representations of IFsignals outputted by ADC 14 or selection unit 25 into baseband signals.

Message detection and decoding unit 18 may be configured to performpreamble detection to detect the presence of ADS-B messages within thereceived data stream. Message detection and decoding unit 18 may also beconfigured to decode the ADS-B messages detected within the receiveddata stream. For example, message detection and decoding unit 18 may beconfigured to perform pulse-position modulation (PPM) signaldemodulation into binary data and to perform error detection andcorrection on the demodulated binary data to decode the ADS-B data.

Configuration of receiver 8 shown in FIG. 4 may utilize multi-channelRFFE 12, multi-channel ADC 14, selection unit 25, and single-channel DBE20.

As discussed above, selection unit 25 may select a single signal that isfurther processed by single-channel DBE 20. As such, DBE 20 may output asingle ADS-B message carried by the selected signal.

Traffic computer (not depicted in FIG. 4) of aircraft 2 may processADS-B data (among other data inputs) outputted by receiver 8 and mayoutput application specific data to a communication bus (not depicted inFIG. 4). For example, traffic computer may output positions of nearbyaircraft to a communication bus. That data may be utilized either by anoutput device, such as a display device, which may be viewed by pilotsof aircraft 2, or it may be processed by a software application, such asa collision avoidance application.

FIG. 5 is a functional block diagram illustrating an example receiver 8for selecting a RF signal to process. As shown in FIG. 5, receiver 8 mayinclude RF switch 26, RFFE 12, ADC 14, and DBE 20. DBE 20 may includepreprocessing unit 16 and message detection and decoding unit 18.

Receiver 8 may comprise any suitable arrangement of hardware, software,firmware, or any combination thereof, to perform the techniquesattributed to receiver 8, RF switch 26, RFFE 12, ADC 14, preprocessingunit 16, message detection and decoding unit 18, and DBE 20 herein. Forexample, receiver 8 may include any one or more microprocessors, digitalsignal processors (DSPs), application specific integrated circuits(ASICs), field programmable gate arrays (FPGAs), or any other equivalentintegrated or discrete logic circuitry, as well as any combinations ofsuch components. Although RF switch 26, RFFE 12, ADC 14, preprocessingunit 16, and message detection and decoding unit 18 are described asseparate modules, in some examples, RF switch 26, RFFE 12, ADC 14,preprocessing unit 16, and message detection and decoding unit 18 can befunctionally integrated. For example, preprocessing unit 16, and messagedetection and decoding unit 18 may be implemented in the same hardwarecomponent. In some examples, RF switch 26, RFFE 12, ADC 14,preprocessing unit 16, and message detection and decoding unit 18 maycorrespond to individual hardware units, such as ASICs, DSPs, FPGAs, orother hardware units, or one or more common hardware units.

In the example of FIG. 5, two or more antenna elements of antennaelements 4 may each receive an RF signal. Antenna elements 4, in someexamples, may comprise antenna elements of a TCAS antenna. Each elementof antenna elements 4 may be a directional antenna element thatcorresponds to at least one of a plurality of sectors of a sectorizedantenna. Each of antenna elements 4 may be operably coupled to RF switch26. RF switch 26 may be configured to select one RF signal out of the RFsignals received by antenna elements 4. For example, RF switch 26 mayselect the one RF signal based on the power level of the RF signals(e.g., select the strongest RF signal).

RFFE 12 of receiver 8 may be operably coupled to RF switch 26 via, forexample, coaxial cable 11. RFFE 12 may process and convert the RF signalstream received from RF switch 26 into an analog intermediate frequency(IF) signal.

ADC 14 of receiver 8 may be operably coupled to RFFE 12 to receive ananalog IF signal from RFFE 12 and to convert the received analog IFsignal into a digital representation of the IF signal.

Preprocessing unit 16 may be configured to perform filtering,decimation, and downconversion of the digital representation of the IFsignal outputted by ADC 14 into a baseband signal.

Message detection and decoding unit 18 may be configured to performpreamble detection to detect the presence of ADS-B messages within thebaseband signal. Message detection and decoding unit 18 may also beconfigured to decode the ADS-B messages detected within the basebandsignal. For example, message detection and decoding unit 18 may beconfigured to perform pulse-position modulation (PPM) signaldemodulation into binary data and to perform error detection andcorrection on the demodulated binary data to decode the ADS-B data.

Configuration of receiver 8 shown in FIG. 5 may utilize RF switch 26,single-channel RFFE 12, single-channel ADC 14, and single-channel DBE20. This configuration may be less complex than the one shown in FIG. 4as the receiver 8 comprises single-channel processing except for RFswitch 26.

The traffic computer (not depicted in FIG. 5) of aircraft 2 may processADS-B data (among other data inputs) outputted by receiver 8 and mayoutput application specific data to a communication bus (not depicted inFIG. 5). For example, traffic computer may output positions of nearbyaircraft to a communication bus. That data may be utilized either by anoutput device, such as a display device, which may be viewed by pilotsof aircraft 2, or it may be processed by a software application, such asa collision avoidance application.

FIG. 6 is a functional block diagram illustrating the example duplicitycheck unit 22 of FIG. 2 in further detail. As shown in FIG. 6, duplicitycheck unit 22 may include buffers 30A-30D (“buffers 30”), comparatorunit 32, and cyclic buffer 34. In an example where components ofreceiver 8 may process four RF signal streams received from four antennaelements 4A-4D, duplicity check unit 22 may include four buffers 30A-30Dto continuously store ADS-B messages data decoded from the correspondingRF signal streams, received by corresponding antenna elements 4A-4D andprocessed by corresponding channel of multi-channel RFFE 12, ADC 14, andDBE 20.

ADS-B message data decoded by individual channels of DBE 20 may becontinuously stored in corresponding buffers 30A-30D. For example, ADS-Bmessage data decoded by the second channel of DBE 20 may be stored inbuffer 30B. Comparator unit 32 may periodically load data from allbuffers 30A-30D and may compare loaded ADS-B data with all ADS-B dataretained in cyclic buffer 34. For 112-bit ADS-B messages, comparatorunit 32 may compare the 88-bit data bits, the 24-bit error correctiondata bits (also known as parity bits), or the entire 112 bits of theADS-B message. For example, comparator unit 32 may determine that oneparticular ADS-B message (loaded from buffers 30) is a duplicate ofanother ADS-B message retained in cyclic buffer 34 if the 24 parity bitsof the particular ADS-B message are the same as the 24 parity bits ofthe another ADS-B message. In another example, comparator unit 32 maydetermine that one particular ADS-B message (loaded from buffers 30) isa duplicate of another ADS-B message retained in cyclic buffer 34 if the88-bit data bits of the particular ADS-B message are the same as the88-bit data bits of the another ADS-B message. In another example,comparator unit 32 may determine that one particular ADS-B message(loaded from buffers 30) is a duplicate of another ADS-B messageretained in cyclic buffer 34 if all the 112 bits of the particular ADS-Bmessage are the same as all the 112 bits of the another ADS-B message.

If the ADS-B message data loaded from buffers 30 is not a duplicate ofany previous ADS-B messages data retained in cyclic buffer 34,comparator unit 32 may output the ADS-B message data and may also storethe ADS-B message data in to cyclic buffer 34. Conversely, if the ADS-Bmessage data loaded from buffers 30 is a duplicate of a previous ADS-Bmessage data retained in cyclic buffer 34, duplicity check unit 22 mayrefrain from outputting the ADS-B message data that is checked bycomparator unit 32. In this way, duplicity check unit 22 may, for aplurality of ADS-B messages decoded by multi-channel DBE 20, determinewhether one particular ADS-B message is a duplicate of another ADS-Bmessage, and, in response to determining that one particular ADS-Bmessage is a duplicate of another ADS-B message, refrain from outputtingmore than one ADS-B message data. The length of cyclic buffer 34 may beadjusted so that a message in the cyclic buffer 34 is not overwrittenbefore there is still a possibility it will be compared to a duplicatemessage being decoded by individual channels of DBE 20.

FIG. 7 is a functional block diagram illustrating the combining unit 24of FIG. 3 in further detail. As shown in FIG. 7, combining unit 24 mayinclude signal phase estimation unit 36, multiplier units 38A-38D(“multiplier units 38”), and adder unit 40. As discussed above withrespect to FIG. 3, combining unit 24 may be configured to combine thedigital representations of IF signals outputted by ADC 14 into a singledigital IF signal that may be processed by single-channel DBE 20.Combining unit 24 may perform a linear combination of each of thedigital representations of the IF signals outputted by ADC 14. Combiningunit 24 may perform phase compensation on the digital representations ofIF signals outputted by ADC 14 to result in a single digitalrepresentation of an IF signal.

In an example where components of receiver 8 may receive four RF signalsfrom four antenna elements 4A-4D, combining unit 24 may receive as inputfour digital representations of IF signals outputted by ADC 14. Signalphase estimation unit 36 may, for each of the four signals received bycombining unit 24, determine a combining coefficient, such as via aproper method. Because the four signals may each carry the same ADS-Bmessage but are out of phase with respect to each other, signal phaseestimation unit 36 may determine a combining coefficient for each of thefour signals that compensates for the phase differences between each ofthe four signals. Each signal may be multiplied with its combiningcoefficient via multiplier units 38 to result in signals that are inphase with each other. The in-phase signals may be added together viaadder unit 40 to result in a digital representation of a combined IFsignal that may be further processed by DBE 20.

FIG. 8 is a flow diagram illustrating an example technique for receivingand decoding ADS-B messages according to aspects of the presentdisclosure. While FIG. 8 is described with respect to antenna elements 4and receiver 8, in other examples, the technique shown in FIG. 8 can beimplemented by any other suitable systems or components alone or incombination with antenna elements 4 and receiver 8.

In accordance with the technique shown in FIG. 8, a plurality of antennaelements 4 may receive a plurality of signals, wherein each of theplurality of antenna elements 4 may correspond to at least one of aplurality of sectors of a sectorized antenna (82). Receiver 8 mayprocess each of the plurality of signals in parallel, including decodingone or more messages from the plurality of signals (84). Receiver 8 mayoutput at least one of the one or more messages (86).

In some examples, receiver 8 processing one or more of the plurality ofsignals may include receiver 8 processing each of the plurality ofsignals in parallel. In some examples, receiver 8 processing one or moreof the plurality of signals may include receiver 8 processing each ofthe plurality of signals to decode a plurality of messages from theplurality of signals. In some examples, duplicity check unit 22 maydetermine whether a one particular message of the plurality of messagesis a duplicate of another message of the plurality of messages.Duplicity check unit 22 may, in response to determining that theparticular message is a duplicate of another message, refrain fromoutputting more than one instance of ADS-B message data.

In some examples, receiver 8 processing one or more of the plurality ofsignals may include receiver 8 combining the plurality of signals toresult in a combined signal and decoding a message from the combinedsignal. In some examples, receiver 8 outputting the one or more messagesmay include receiver 8 outputting the message.

In some examples, receiver 8 processing one or more of the plurality ofsignals may include receiver 8 selecting one of the plurality of signalsand decoding a message from the selected one of the plurality ofsignals. In some examples, receiver 8 outputting the one or moremessages may include receiver 8 outputting the message.

In some examples, the plurality of antenna elements 4 comprises antennaelements of a traffic collision avoidance system (TCAS) antenna. In someexamples, receiver 8 comprises a TCAS computer. In some examples, theone or more messages comprise one or more automatic dependentsurveillance-broadcast (ADS-B) messages.

The techniques of this disclosure may be implemented in a wide varietyof devices. Any components, modules or units have been describedprovided to emphasize functional aspects and does not necessarilyrequire realization by different hardware units. The techniquesdescribed herein may also be implemented in hardware, software,firmware, or any combination thereof. Any features described as modules,units or components may be implemented together in an integrated logicdevice or separately as discrete but interoperable logic devices. Insome cases, various features may be implemented as an integrated circuitdevice, such as an integrated circuit chip or chipset.

If implemented in software, the techniques may be realized at least inpart by a computer-readable medium comprising instructions that, whenexecuted in a processor, performs one or more of the methods describedabove. The computer-readable medium may comprise a tangiblecomputer-readable storage medium and may form part of a larger product.The computer-readable storage medium may comprise random access memory(RAM) such as synchronous dynamic random access memory (SDRAM),read-only memory (ROM), non-volatile random access memory (NVRAM),electrically erasable programmable read-only memory (EEPROM), FLASHmemory, magnetic or optical data storage media, and the like. Thecomputer-readable storage medium may also comprise a non-volatilestorage device, such as a hard-disk, magnetic tape, a compact disk (CD),digital versatile disk (DVD), Blu-ray disk, holographic data storagemedia, or other non-volatile storage device.

The memory described herein that defines the physical memory addresses,which may be used as part of the described encryption, may also berealized in any of a wide variety of memory, including but not limitedto, RAM, SDRAM, NVRAM, EEPROM, FLASH memory, dynamic RAM (DRAM),magnetic RAM (MRAM), or other types of memory.

The term “processor,” as used herein may refer to any of the foregoingstructure or any other structure suitable for implementation of thetechniques described herein. In addition, in some aspects, thefunctionality described herein may be provided within dedicated softwaremodules or hardware modules configured for performing the techniques ofthis disclosure. Even if implemented in software, the techniques may usehardware such as a processor to execute the software, and a memory tostore the software. In any such cases, the computers described hereinmay define a specific machine that is capable of executing the specificfunctions described herein. Also, the techniques could be fullyimplemented in one or more circuits or logic elements, which could alsobe considered a processor.

FIGS. 1B, 2, 3, 4, 5 depict examples of some possible implementations.However, various combinations of these example implementations are alsopossible as well as additional implementations not described herein thatalso utilize techniques involving sectorized antennas described herein.

The techniques of this disclosure may also be utilized for improvedreception of several surveillance signals, and may not be limited to theexamples described herein regarding the improved reception of ADS-Bsignals.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is: 1: A method comprising: receiving, by a plurality ofantenna elements, a plurality of signals carrying one or more automaticdependent surveillance-broadcast (ADS-B) messages and one or moresignals that do not carry ADS-B messages, wherein each of the pluralityof antenna elements correspond to at least one of a plurality of sectorsof a sectorized antenna; converting, by a multi-channel radio frequencyfront end (RFFE) of a receiver, the plurality of signals to a pluralityof intermediate frequency signals in parallel; converting, by one ormore analog to digital converters of the receiver, the plurality ofintermediate frequency signals to a plurality of digital signals;processing, by a multi-channel digital back-end of the receiver, each ofthe plurality of digital signals in parallel, including combining theplurality of digital signals to result in a combined signal and decodingan ADS-B message from the combined signal; outputting, by the receiver,the decoded ADS-B message. 2: The method of claim 1, wherein: theplurality of antenna elements comprises antenna elements of a trafficcollision avoidance system (TCAS) antenna; and a TCAS unit incorporatesthe receiver. 3: The method of claim 1, wherein the one or more ADS-Bmessages comprise a plurality of ADS-B messages, further comprising:determining whether a particular ADS-B message in the plurality of ADS-Bmessages is a duplicate of other ADS-B messages in the plurality ofADS-B messages; and in response to determining that the particular ADS-Bmessage is a duplicate of another ADS-B message, refrain fromoutputting, by the duplicity check unit, more than one instance of ADS-Bmessage data of the particular ADS-B message. 4: A system comprising: aplurality of antenna elements configured to receive a plurality ofsignals carrying one or more automatic dependent surveillance-broadcast(ADS-B) messages and one or more signals that do not carry ADS-Bmessages, wherein each of the plurality of antenna elements correspondto at least one of a plurality of sectors of a sectorized antenna; and areceiver comprising: a multi-channel radio frequency front end (RFFE)configured to convert the plurality of signals to a plurality ofintermediate frequency signals in parallel; one or more analog todigital converters configured to convert the plurality of intermediatefrequency signals to a plurality of digital signals; and a multi-channeldigital back-end configured to process each of the plurality of digitalsignals in parallel, including combining the plurality of digitalsignals to result in a combined signal and decoding an ADS-B messagefrom the combined signal; and wherein the receiver is further configuredto output the decoded ADS-B message. 5: The system of claim 4, wherein:the plurality of antenna elements comprises antenna elements of atraffic collision avoidance system (TCAS) antenna; and the receivercomprises a TCAS computer. 6: The system of claim 4, wherein the one ormore ADS-B messages comprise a plurality of ADS-B messages, furthercomprising: a duplicity check unit configured to: determine whether aparticular ADS-B message in the plurality of ADS-B messages is aduplicate of other ADS-B messages in the plurality of ADS-B messages;and in response to determining that the particular ADS-B message is aduplicate of another ADS-B message, refrain from outputting more thanone instance of ADS-B message data of the particular ADS-B message.